The use of carbonaceous materials for sound and thermal barriers is now known. The materials in the form of battings and mats are now being proposed for use in areas subjected to high temperatures and degrading gases, especially oxidizing gases.
It has been proposed to coat the carbonaceous fibers with ceramic and metallic materials to provide protection for the fibers against these oxidizing gases. However, such materials can be expensive, difficult to apply, add significant weight and can sometimes alter the low water retention properties of the structure. Furthermore, the resulting structure is relatively hard and does not have the flexibility or feel of the original fibers.
The prior carbonaceous materials have also been useful to provide a flame barrier. However, the flame barrier in many cases is effective only against static flames. There are occasions when it is desirable to provide protection against short periods of dynamic flames which are a result of pressure forces, wind velocities of the like. Such flames can cause physical erosion of a flame barrier.
K. Tanaka et al, U.S. Pat. No. 4,308,371 granted Dec. 29, 1981 and B. E. Yoldas et al, U.S. Pat. No. 4,814,017 granted Mar. 21, 1989, which are herewith incorporated by reference, disclose organoalkoxsilanes which may be used in the present invention.
E. L. Yuan, U.S. Pat. No. 3,811,997, granted May 21, 1974, discloses smoke and flame resistant structural articles for use in aircrafts. The articles can be of a laminate or a honeycomb construction. The articles are provided with a thin film of polyimine or polyamide to retard combustion of the underlying laminate and reduce smoke effusion from any burning that does occur.
I. K. Park, U.S. Pat. No. 3,914,494, granted Oct. 21, 1975, discloses a material for use, for example, as a facing sheet for a sandwich liner for noise suppression in a jet engine. The lightweight material includes woven carbon fibers in a resin matrix. The resin can be phenolic or a polyimide. Burning phenolic resins produce highly irritating smoke.
U.S. Pat. No. 4,642,664 to Goldberg et al, which is herewith incorporated by reference, discloses polyaromatic precursor and carbonaceous materials which may be used in the present invention.
U.S. Pat. No. 4,837,076 to McCullough et al, which is herein incorporated by reference, discloses a class of carbonaceous fibers which can be used in connection with the present invention.
U.S. Pat. No. 4,879,168 to McCullough et al, discloses the synergism of carbonaceous fibers blended with thermosetting resins with regard to fire resistance.
U.S. Pat. No. 4,255,483, to N. R. Byrd et al discloses an acoustic firewall for use in environments such as an aircraft engine nacelle. The firewall includes a graphite fiber or glass cloth embedded in a silica-containing polyimide resin. The presence of the silica is described as being necessary to provide the polyimide resin and the firewall with the desired stability in the presence of a fire and with low thermal conductivity.
The carbonaceous materials of the invention according to the test method of ASTM D 2863-77 have an LOI value greater than 40. The test method is also known as "oxygen index" or "limited oxygen index" (LOI). With this procedure the concentration of oxygen in O.sub.2 /N.sub.2 mixtures is determined at which a vertically mounted specimen is ignited at its upper end and just continues to burn. The size of the specimen is 0.65.times.0.3 cm with a length from 7 to 15 cm. The LOI value is calculated according to the equation: ##EQU1##
The LOI values of different materials are as follows:
______________________________________ polypropylene 17.4 polyethylene 17.4 polystyrene 18.1 rayon 18.6 cotton 20.1 nylon 20.0 polycarbonate 22 rigid polyvinyl chloride 40 stabilized polyacrylonitrile &gt;40 graphite 55 ______________________________________
The carbonaceous materials of the invention can also be characterized by having a thermal conductivity of less than 1 BTU ft/Hr ft.sup.2 .degree.F.
The measurement of char formation as discussed herein is made using a standard thermogravimetric analysis apparatus that is adapted so as to perform the analysis in a nitrogen atmosphere. The apparatus is described in Encyclopedia of Polymer Science, Vol. 14, p. 21, John Wiley & Son, 1971, which is incorporated herein by reference.
The measurement is performed by loading a sample onto the sample pan of the thermogravimetric analysis apparatus. The sample is then heated in an nitrogen atmosphere at a rate of 10.degree. C./min from ambient temperature to 900.degree. C. The thermogravimetric apparatus records the sample weight remaining versus temperature.
The percent of original weight remaining at 800.degree. C. is taken as the char percentage.
The percent char formation and thermal conductivities of different materials are as follows:
______________________________________ Conductivity % Char ft/Hr/ft.sup.2 .degree.F. ______________________________________ Carbonaceous particles (18.6% N.sub.2) &gt;65 0.1 of invention Carbonaceous particles (16.0 N.sub.2) &gt;65 0.2 of invention KEVLAR 60 &lt;1 KODEL 410 polyester 10 &lt;1 Polyacrylonitrile 60 &lt;1 Oxidized polyacrylonitrile 60 &lt;1 THORNEL 300* carbon fiber &gt;95 4.84 Cotton &gt;30 &lt;1 Rayon &lt;50 &lt;1 Polycarbonate 22 &lt;1 Polyethylene terephthalate 10 &lt;1 Carbon particles &gt;90 2.5 THORNEL Graphite fiber P758** &gt;95 106.48 ______________________________________ *1K/3K/6K/15K Carbon yarn of Amoco Corp., Danbury CT. **2K/4K Carbon yarn derived from pitch of Amoco Corp., Danbury CT.
It is understood that the term "fire resistant" as used herein relates to any one of the characteristics of flame arresting, flame retarding, fire shielding and fire barrier.
An article is considered to be flame retarding to the extent that once an igniting flame has ceased to contact unburned parts of the textile structure, the article has the inherent ability to resist further propagation of the flame along its unburned portion, thereby stopping the internal burning process. Recognized tests to determine whether a textile article is flame retarding are, inter alia, the American Association of Textile Chemists and Colorists Test Method 34-1966 and the National Bureau of Standards Test described in DOC FF 3-71.
An article is considered to be "fire shielding" if it is capable of deflecting flames and the radiation therefrom in a similar manner as aluminum coated protective garments, which are known in the art.
Fire barriers have the capability of being non-flammable, flame retarding and providing thermal insulation characteristics.
The term "polymeric" used herein includes natural substances as well as other organic polymeric materials including organosilicone polymers.
"Static flames" as herein recited relates to flames which are subject to substantially little or no pressure, for example, match, candlestick or butane lighter flames.
"Dynamic flames" as herein defined relates to flames which are acting under a pressure such as disclosed in FAR 25.855 Appendix F.
The term "polymer" as used herein relates to the set or cured polymers which can be obtained from the silicone resins or the hydrolyzed partial condensation products of siloxanes such as manufactured by Dow Corning Corporation.
The term "silicone resin" as herein disclosed relates to any precursor material which is capable of being polymerized to form the organosilicone polymers of the invention. The silicone resins include but are not limited to oligomers derived typically by the partial hydrolysis of a silane. The oligomers generally have a backbone of siloxane units and active sites which may be cured thermally and/or hydrolytically to form the organosilicone polymer.
The resins further include the precursor silane compounds which are capable of forming organosilicone polymers through a free radical condensation reaction or a heat condensation reaction. Typically, the heat condensation and/or free radical condensation reactions are performed utilizing silanes having epoxy or vinyl moieties.
The term "reinforcement scrim" relates to metallic, glass or fibrous structures which are woven, non-woven, knit, or the like, that are utilized to provide a mechanical or physical reinforcement to structures against dynamic forces. The term includes composite structures containing unidirectional fibers.
The term "carbonaceous fibers" as used herein relates to polymeric fibers whose carbon content has been irreversibly increased as a result of a chemical reaction such as a heat treatment, as disclosed in U.S. Pat. No. 4,837,076.
The term "non-graphitic" as used herein relates to those carbonaceous materials having an elemental carbon content of less than 92 percent (%), which are substantially free of oriented carbon or graphite microcrystals of a three dimensional order, and as further defined in U.S. Pat. No. 4,005,183, which is herein incorporated by reference.
It should be understood that the term "particles" as used herein is intended to include powders, platelets, and the like.
The non-linear carbonaceous fibers preferably used in the invention are resilient, shape reforming and have a reversible deflection greater than about 1.2:1. It should be understood that the reversible fiber deflection comprises two components, pseudoelongation and fiber elongation. Pseudoelongation results from the non-linear configuration and/or false twist imposed on the fiber. Fiber elongation is the elongation to fiber break after the fiber has been made linear.
All percentages referred to herein are in percentage by weight.